“I looked him in his eyes while he killed my friends I hope he rots in hell for eternity,” he wrote on Instagram.

“The guy you see is the murderer and the shots are him shooting people trying to get out the windows.”

Image:People comfort each other outside the bar

A number of gunshots can be heard in the footage at the country music bar.

The video then showed Mr Knapp fleeing through a door and running down a street, shouting that there were still people trapped in the club in the city of Thousand Oaks.

As the video was released, it emerged one of the victims of the massacre had survived last year’s mass shooting in Las Vegas, where 59 people were killed at a country music festival.

The mother of Telemachus Orfanos, 27, said her son had died inside Borderline. A video shows her shaking with rage as she pleads for gun control.

“I don’t want prayers. I don’t want thoughts,” she says. “Pass gun control so no one else has a child that doesn’t come home.”

Image:Witnesses say Ian Long used smoke bombs in the attack

Police are currently investigating Long, a decorated marine who served in Afghanistan, who killed himself after the shooting.

Witnesses said he wore something like a ski mask as he opened fire in the packed club at around 11.20pm on Wednesday evening.

“There were people hiding in restrooms, there were people hiding in attics,” said Ventura County sheriffGeoff Dean.

“It’s a horrific scene in there. There is blood everywhere”.

Image:Armed response units surround the area

Among those killed was Sergeant Ron Helus, who had served 29 years in the police and was due to retire, and died responding to the incident call.

The officer was on the phone to his wife when the emergency call came in, telling her: “Hey I gotta go handle a call. I love you. I’ll talk to you later.”

Cody Coffman, 22, was confirmed to have died during the attack by his father, Jason.

Speaking through tears, Mr Coffman said: “I talked to him last night, before he headed out the door. First thing I said was, ‘please don’t drink and drive’. Last thing I said was, ‘son, I love you’. That was the last thing I said.”

0:45

Video:Jason Coffman confirms that his 22-year-old son Cody was killed

Survivors describe hiding and fleeing after shots were heard, and a panicked rush to try and escape through windows which had been broken with chairs.

Police believed Long fired around 30 shots with a Glock 21 handgun with an extended magazine designed to hold extra bullets – something that is illegal in California.

A trail of blood was visible on the street at the entrance of the venue. A number of victims with serious injuries were rescued and taken to hospital.

Image:Mourners lined the streets as the body of Sgt Ron Helus was carried

Police said they had previous contact with the gunman.

In April, he was found irate and acting irrationally when they were were called to his home. A mental health crisis team decided Long did not need to be taken into custody.

His motive is so far unknown and police were searching his property for clues.